Various methods of calculating the amount of air flowing into a cylinder in an internal combustion engine have been proposed, and according to a known method among them, using an air intake valve model, a cylinder flowing air amount is calculated based on the pressure of an intake pipe (Refer to, for example, Patent Literature 1). According to the calculation method using the air intake valve model, the cylinder flowing air amount when the air intake valve is opened, is calculated in consideration of volumetric efficiency ηv of the internal combustion engine.